1. Field of the Invention
The present invention relates generally to a switch mechanism for a key-entry use and, more particularly, to a key-entry switch (hereinafter referred to as a key switch) preferably used for relatively thin keyboards incorporated as input terminals in data processing equipment such as personal computers or word processors.
2. Description of the Related Art
When data processing equipments, such as personal computers or word processors, etc., are required to be downsized for portable use, it is also required for keyboards incorporated therein to have a reduced height or thickness. However, as a solution for reducing the thickness of the keyboard, if the stroke of each of plural key switches provided in the keyboard is reduced, proper key-entry operations may be made difficult. Accordingly, it has been desired to provide a key switch in which the height of the keyboard can be reduced while maintaining the stroke of the key switch at a predetermined distance to ensure good and stable operational properties thereof.
FIGS. 1, 2A and 2B show an example of a conventional key switch for use in a relatively thin keyboard. As shown in FIG. 1, the conventional key switch includes a key top 2 adapted to be keyed or pushed down by an operator's finger, a base 3 disposed beneath the key top 2, a pair of gear-link members 1 for supporting the key top 2 above the base 3 and directing it in the vertical or up-and-down direction, a sheet-like switch (hereinafter referred to as a membrane switch) 5 arranged beneath the base 3, an elastic actuating member (not shown) located between the key top 2 and the membrane switch 5 so as to open and close the membrane switch 5 corresponding to the vertical or up-and-down movement of the key top 2, and a support panel 4 disposed beneath the membrane switch 5 to hold it between the base 3 and the support panel 4.
The pair of gear-link members 1 are assembled into a generally reverse V-shape in a side view and meshed with each other at the toothed ends 13 thereof. Each of the gear-link members 1 includes a sliding bar 11 and a pair of arms 12 joined perpendicularly to the bar 11 near the opposed ends of the latter. Each arm 12 is provided at the distal or toothed end 13 thereof with at least one tooth 14 which radially projects from the circumferential edge of the toothed end 13. Slide shafts 16 are formed at the opposed ends of the bar 11, and pivot shafts 15 are formed near the toothed ends 13 of the arms 12 to project on the same sides as, and in parallel to, the slide shafts 16. The gear-link members 1 are pivotably interconnected with each other by intermeshings between one tooth 14 of the first arms 12 of respective gear-link members 1 and two teeth 14 of the second arms 12 of respective gear-link members 1.
The key top 2 is provided at an inner surface thereof with a pair of pivot supports 22, each of which includes two bearing holes 21. The pivot supports 22 are located in such a manner that the respective two bearing holes 21 are opposite to each other. The pivot shafts 15 formed near the toothed ends 13 of the arms 12 of each gear-link member 1 are pivotably fitted or received in the bearing holes 21 of the respective pivot supports 22 (see FIG. 2A).
The base 3 is provided with a center opening 31 into which the pair of gear-link members 1 can be inserted, and two pairs of slide supports 32 arranged along two opposed inner edges defining the center opening 31 and partially projecting above the center opening 31. Each of the slide supports 32 is provided at the end thereof with a stopper 33, and defines a bearing slot between the membrane switch 5 and the slide support 32. The slide shafts 16 formed at the opposed ends of the bar 11 of each gear-link member 1 are slidably fitted or received in the bearing slots of the respective slide supports 32 (see FIG. 2A). The stopper 33 of each slide support 32 acts to prevent each slide shaft 16 falling-out from the bearing slot.
In this structure, the key top 2 is permitted to be subjected to a parallel displacement in a substantially vertical direction on the base 3, while keeping a predetermined posture of the key top 2. Also, it is possible to reduce the entire height of the key switch, while maintaining a predetermined amount of the stroke of the key switch.
The membrane switch 5 is structured from two flexible printed circuit boards 52, of which conductive patterns are arranged opposite to each other through a spacer 51. A switching element formed from a pair of conductive contacts opposed to each other through a gap is positioned beneath the key top 2.
The elastic actuating member (not shown) is a dome-like member made from a rubber material. When no external force is applied to the key top 2, the elastic actuating member supports the key top 2 and urges the latter toward an initial position vertically upwardly away from the base 3 (see FIG. 2A). During this state, the slide shafts 16 of each gear-link member 1 are biased along the bearing slots of the respective slide supports 32, and are located near the stoppers 33 of the slide supports 32.
When the key top 2 is pushed downward by a key-entry operation, the elastic actuating member is elastically deformed while exerting biasing or elastic restoring force to the key top 2 in an upward direction. During this operation, the gear-link members 1 are pivoted in an interlocked manner, and the slide shafts 16 of each gear-link member 1 are shifted in the bearing slots of the slide supports 32 to enlarge the distance from the slide shafts 16 of the counterpart gear-link member 1. Then, the interior surface of the dome upper end of the elastic actuating member pushes the outer surface of the upper flexible printed circuit board 52, so as to close or turn-on the membrane switch 5.
When downward pushing force applied to the key top 2 is released, the elastic actuating member is elastically restored, so as to return or push-up the key top 2 to the initial position and to open or turn-off the membrane switch 5. During this operation, the gear-link members 1 are pivoted in a reverse direction in an interlocked manner, and the slide shafts 16 of each gear-link member 1 are shifted in the bearing slots of the slide supports 32 to reduce the distance from the slide shafts 16 of the counterpart gear-link member 1.
In the above-mentioned conventional key switch including the gear-link members, it is generally required to provide the toothed ends of the arms of each gear-link member with a dimension sufficient to enable a smooth rotation under the intermeshed condition where at least one tooth of each toothed end are intermeshed with the counterpart at least one tooth. This dimensional requirement of the gear-link member may hamper the reduction of the height or thickness of the keyboard.
Also, it is generally required to highly precisely form the at least one tooth of the toothed end, in order to establish the smooth rotation under the intermeshed condition of the gear-link members. However, when the gear-link member is miniaturized to a certain degree, it is made difficult to precisely form the at least one tooth of the toothed end. As a result, the operational properties of the key switch may be deteriorated, and the production cost for the keyboard may be increased.